This invention relates to a diode laser, and, more particularly, to a diode laser structure that has been thermally stabilized by passing currents through heater strips along the sides of the diode laser cavity.
Typical diode laser pixel times for high speed printers are in the order of 10 to 100 nanoseconds. When the laser is turned on, adiabatic heating of the diode laser cavity occurs due to the inefficiency of the conversion of electrical energy into emitted light. The heat dissipates over time periods on the order of 10 to 100 microseconds. This difference in time constants will cause the temperature of the typical diode laser cavity to vary with the pattern of the data being written. This effect gives rise to pattern dependent instability. For example, if the laser has been off for a period of several microseconds, and it is turned on for a single pixel time, the laser cavity will be at some temperature T, when it emits the light for that single pixel. If, however, the laser has been on continuously, or quasi-continuously, for a period of several hundred microseconds, is turned off for just a few pixels, and is then turned back on again, the laser cavity will be at a higher temperature, T+dT. dT can be on the order of 1 to 10 degrees Centigrade, depending on the efficiency and structure of the laser.
This change in the temperature of the laser cavity can change both the power emitted and the wavelength of the emission. These changes are detrimental to some applications of diode lasers. In particular, the instability in the wavelength of the emission may cause a focus shift and degradation of the image quality.
A technology known as distributed feedback lasers is currently being pursued to stabilize the wavelength of the emission, by using Bragg scattering to define the laser cavity, instead of mirrors. This technology, which is capable of reducing the wavelength shift, but not the change in power emitted, has resulted in relatively expensive diode lasers.
Typical prior art diode laser structures use a heat sink to remove heat from the diode laser structure during light emission. The heat sink temperature is maintained at a constant level by using a Peltier or thermo-electric cooler. Because of the thermal resistance between the diode laser cavity and the heat sink, this technique is not capable of maintaining the diode laser cavity at a constant transient temperature. The heat sink helps maintain an average temperature within the diode laser cavity. The laser pixel times for high speed printers occur too fast and over too short periods of time for the heat sink or Peltier or thermo-electric cooler to respond to, thus resulting in temperature fluctuations from pulse to pulse within the laser cavity.
It is an object of this invention to provide a novel means to stabilize the temperature of a diode laser cavity and thus to stabilize the power emitted and the wavelength of the light emission from that diode laser cavity.
It is another object of this invention to provide a means to stabilize the temperature of a diode laser cavity at the hotter, higher temperature at which the laser cavity is emitting light even when the diode laser cavity is not emitting light.
It is another object of this invention to provide a means to stabilize the temperature of a diode laser cavity at a constant transient temperature and to stabilize the temperature of a diode laser cavity from pulse to pulse.